The field of the invention is imaging by electrostatic techniques such as xerography or electrofax but includes printing as it is known in high speed presses. Specifically the invention is concerned with the provision of an endless belt or cylinder which has a conductive base or substrate and a coating of photoconductive material on the surface of the belt or cylinder. Hereafter the word "sleeve" will be used to designate a generic form including both belt and cylinder.
In the art of electrostatics there have been commercial structures which operate on the same basic principles to achieve images of objects. The basic concept consists of charging the surface of a photoconductive material which is capable of holding the charge in darkness, then exposing the surface to a radiant energy pattern such as a projected object, then developing the resulting latent image by means of toner. In xerography the toned image is transferred to a receptor while in electrofax the toned image is fixed as by fusing and the entire electrophotographic member becomes the article which emerges from the apparatus as a "copy" of the object.
The materials which have become commercially important in these fields are amorphous selenium, usually deposited as a layer of considerable thickness onto a rigid metal drum; zinc oxide particles in a matrix of organic material carried on a sheet of conductive paper; various photoconductive dyes on different kinds of substrate members; and even a slurry of cadmium sulfide in an organic matrix locked beneath a plastic sheet. The latter material is not chargeable per se since it is incapable of holding a charge but rather its plastic covering is chargeable and the cadmium sulfide slurry acts only in the photoconductive mode to assist in discharging increments of the plastic covering during exposure.
So far as known, available photoconductive materials are slow in response, have low resolution, require high voltages for charging and intense light for discharging, cannot be fully discharged and hence have objectionable background, and have other disadvantages. As such they are not suitable for use in any kind of high speed, high quality, economical imaging apparatus. For instance, high speed printing and multiple copy reproducing cannot be effected with known materials.
Recently a new material has been developed which is disclosed in U.S. Pat. No. 4,025,339 which not only overcomes all of the disadvantages of the prior photoconductive materials but has unusual benefits and attributes which never before existed. U.S. Pat. No. 4,025,339 is incorporated herein by reference and the disclosure thereof should be considered included herein.
The preferred form of the material of the invention comprises cadmium sulfide of ultrapure variety, with or without dopants, sputtered in an r.f. sputtering apparatus according to the teachings of the referenced patent.
In using the material in the combination comprising the invention herein several purposes are served. In duplicating or convenience copiers a relatively rigid drum can be utilized and the latent image formed on the drum, toned and the toner transferred to a web or sheet of paper or fabric or similar receptor after which the drum is cleaned, re-charged, re-exposed, etc., the cycle being repeated again and again for each copy.
In apparatus which requires that a flat planar member be available for the projection of an image thereon, either directly or through the member as for example in a machine which is intended to project large images onto the photoconductive material, the photoconductive material is deposited on a flexible cylinder that is shaped to provide an oval belt when it is installed in the machine. It may be transparent. The machine may be used by forming the toned image on the sleeve and transferring the image to another electrophotographic member which becomes the printing plate or transferring the image from the belt to a paper member which can thereafter be used as a copy or for other purposes.
For printing presses the sleeve or belt may be imaged and the image toned and fixed to provide a primary toned image on the photoconductive surface after which the sleeve or belt can be charged in light to charge only the surface of the fixed toner after which secondary toner can be picked up from a suitable fountain and transferred to a receptor.
The cylinders or belts can be sputtered directly in sputtering apparatus. The rigid cylinders are easily machined or cast. The belts or flexible sleeves can be formed in several ways including shaping flat members on heated mandrels or directly extruding the plastic substrates in plastic extruding machines onto mandrels which preserve their shape until cooled.